Composition and Ultrastructure of Leaf Cuticles From Fruit Trees, Relative to Differential Foliar Absorption

Abstract

Differential foliar absorption of chemicals by peach, apple and orange was related to cuticle thickness, weight, surface wax and embedded wax content and to surface wax wettability, ultrastructure and composition. Surface wax concentration, especially on abaxial leaf surfaces, correlated well with resistance to foliar absorption. The abaxial surface wax on peach leaves was built up in layers around and over the guard cells (which are preferred paths of spray entry into leaves) whereas apple and orange guard cells were relatively wax-free. Peach surface waxes were more difficult to wet than orange waxes and, although more polar than orange waxes, may be more resistant to water penetration as they were rich in hydrocarbons and triterpenoids. Enhancement of foliar absorption may require improved partitioning of sprays through the surface waxes or the bypassing of the waxes via stomatal penetration.